This section is intended to introduce various aspects of the art, which may be associated with embodiments of the disclosed techniques. This discussion is believed to assist in providing a framework to facilitate a better understanding of particular aspects of the disclosed techniques. Accordingly, it should be understood that this section is to be read in this light, and not necessarily as admissions of prior art.
Three-dimensional (3D) model construction and visualization commonly employs data stored in a data volume organized as a structured grid or an unstructured grid. Data stored in a data volume may comprise a data model that corresponds to one or more physical properties about a corresponding region that may be of interest. Physical property model construction and data visualization have been widely accepted by numerous disciplines as a mechanism for analyzing, communicating, and comprehending complex 3D relationships. Examples of physical regions that can be subjected to 3D analysis include the earth's subsurface, facility designs, and the human body.
In the field of hydrocarbon exploration, analysis of a reservoir's connectivity facilitates characterizing the reservoir. Moreover, connectivity analysis may affect decisions made in all phases of hydrocarbon resource development of an asset's life cycle, such as exploration and production. Connectivity assessments can affect decisions such as determining optimal well locations in addition to the management reservoir decisions.
In one technique, a set of rules and processes allows geologists to identify compartments from reservoir geometry. Typically, compartment identification starts with structure maps. Structural features, stratigraphic features, and the limits of top seal or base seal define compartment boundaries. Even without knowledge of fluid contacts, depths, and pressure conditions, one can identify potential compartment boundaries from the maps based on a few simple rules of the structural and stratigraphic features. That is, one can evaluate the relevance of compartment boundaries defined by top-seal or base-seal. Traditional spill points on convex-upward closures and down-dip tips of faults or other structural or stratigraphic barriers are only relevant on top-of-reservoir maps. Break-over points, including those associated with concave-upward closures and up-dip tips of faults or other structural or stratigraphic barriers, are only relevant on base-of-reservoir maps. Even though the rules to identify compartments based on the structure maps are relatively simple, the process of identification typically relies on the geologists' manual identification of compartment boundaries and contact relations among boundaries based on the contour or cross section displays of structural surfaces.
Current processes for compartment identification rely on geologists' knowledge and step-by-step procedures to first identify compartment boundaries. The contacts from compartment boundaries may then be used to identify the spill-over or break-over points among compartments. The current methods may make handling the uncertainty of the structural and stratigraphic features difficult, if not impossible. Various examples of reservoir connectivity analysis techniques are discussed in the following paragraphs.
U.S. Patent Application Publication No. 2007/0027666 to Frankel discloses methods and systems for characterizing connectivity in reservoir models using paths of least resistance. An embodiment is stated to be related to computer modeling of the transmission of properties, such as the flow of fluids within subsurface geological reservoirs. Further, an embodiment is stated to include a method of evaluating the transmission of a property within a subsurface geologic reservoir using a graph-theory single source shortest path algorithm.
U.S. Patent Application Publication No. 2008/0154505 to Kim, et al. discloses a rapid method for reservoir connectivity analysis using a fast marching method. A model of a portion of the reservoir is stated to be divided into cells, where each cell is stated to have a volume and some attributes, and wherein a speed function is stated to be assigned to a portion of the cells. A reference cell is stated to be chosen. A connectivity between cells in the reservoir is stated to be determined by solving an Eikonal equation that describes the travel time propagation, said propagating front progressing outward from a reference cell until an ending condition is met, said Eikonal equation being solved by a fast marching method with propagation velocity as a function of spatial position being provided by the speed function. Regions of the reservoir are stated to be characterized by their connective quality to the reference cell using the connectivity.
U.S. Pat. No. 6,549,879 to Cullick, et al. discloses determining optimal well locations from a 3D reservoir model. Various constraints are stated to be satisfied. In the first stage, the wells are stated to be placed assuming that the wells can only be vertical. In the second stage, these vertical wells are stated to be examined for optimized horizontal and deviated completions. This solution is stated to be expedient, systematic, and provide a good first-pass set of well locations and configurations. The first stage solution is stated to formulate the well placement problem as a binary integer programming (BIP) problem which uses a “set-packing” approach that exploits the problem structure, strengthens the optimization formulation, and reduces the problem size. Commercial software packages are readily available for solving BIP problems. The second stage is stated to sequentially consider selected vertical completions to determine well trajectories that connect maximum reservoir pay values while honoring configuration constraints including completion spacing constraints, angular deviation constraints, and maximum length constraints. The parameter to be optimized in both stages is stated to be a tortuosity-adjusted reservoir quality. An algorithm is stated to be disclosed for calculating the tortuosity-adjusted quality values.
U.S. Pat. No. 7,069,149 to Goff, et al. discloses a process for interpreting faults from a fault-enhanced 3D seismic attribute volume. The method is stated to include the steps of extracting faults from a 3D seismic attribute cube, and then calculating a minimum path value for each voxel of the 3-D seismic attribute cube. A fault network skeleton is stated to be extracted from the 3D seismic attribute cube by utilizing the minimum path values which correspond to voxels within the 3D seismic attribute cube. The individual fault networks are stated to be labeled, and a vector description of the fault network skeleton is stated to be created. The fault network skeleton is stated to be subdivided into individual fault patches wherein the individual fault patches are the smallest, non-intersecting, non-bifurcating patches that lie on only one geologic fault. The individual fault patches are then stated to be correlated into a representation of geologic faults.
International Patent Application Publication No. WO2007/106244 to Li, et al. discloses a method for quantifying reservoir connectivity using fluid travel times. In the method, fluid travel time models are stated to be constructed from a reservoir model. Then, reservoir connectivity measures are stated to be calculated from the fluid travel time models and analyzed to determine a location for at least one well. Based on the analysis, one or more wells may be drilled and hydrocarbons produced.
L. M. Hirsch et al., “Graph Theory Applications to Continuity and Ranking in Geologic Models”, Computers & Geosciences, Volume 25, Number. 2, p. 127-139, states that most of the currently available analysis tools for geologic modeling cannot easily handle irregularities such as faults, onlap and truncations, or they are strongly limited in the dimensions of the models that are amenable to analysis. The article proposes an algorithmic graph theory for computationally efficient, continuity analysis. This method is stated to treat irregularities in the geologic model including unstructured grids of unequal cell sizes. Geologic models are stated to be transformed from a cell-based representation to a node- and connection-based representation, where both nodes and arcs (connections) can have associated properties. Quantities such as connected components, maximum flow, shortest paths, minimum-cost paths and many other connectivity measures are stated to be determined. These connectivity measures are stated to involve connections whose lengths or values are weighted by reservoir parameters such as porosity and permeability. Because graph algorithms are efficient, connectivity is stated to be rapidly evaluated for different wells that might become important during reservoir development. Graph theory algorithms are stated to be applied to rank the anticipated flow performance of different geologic model realizations, to aid in delineating contiguous regions of similar character for use in up-scaling, as well as to assess how well a scaled-up model preserves the continuity of the original detailed geologic model.
P. J. Vrolijk, et al., “Reservoir Connectivity Analysis—Defining Reservoir Connections and Plumbing”, SPE Middle East Oil and Gas Show and Conference, Kingdom of Bahrain (2005), states that gas, oil, and water fluids in channelized or faulted reservoirs can create complex reservoir plumbing relationships. Variable hydrocarbon contacts can develop when some, but not all, fluids are in pressure communication. Reservoir Connectivity Analysis (RCA) is a series of analyses and approaches to integrate structural, stratigraphic, and fluid pressure and composition data into permissible but non-unique scenarios of fluid contacts and pressures. RCA provides the basis for fluid contact and pressure scenarios at all business stages, allowing the creation of fluid contact and segmentation scenarios earlier in an exploration or development setting, and the identification of by-passed pays or new exploration opportunities in a production setting. Combining conventional structural and fault juxtaposition spill concepts with a renewed appreciation of fluid breakover (contacts controlled by spill of pressure-driven, denser fluid, like water over a dam) and capillary leak (to define the ratio of gas and oil where capillary gas leak determines the gas-oil contact (GOC)), permissible but non-unique scenarios of the full fluid fill, displacement, or spill pathways of a hydrocarbon accumulation are defined, comprising single or multiple reservoir intervals.
Additional examples of known reservoir data analysis techniques can be found in U.S. Pat. No. 6,823,266 to Czernuszenko et al., “Reservoir Connectivity: Definitions, Strategies, and Applications” by M. Meurer et al., and PCT Application PCT/US2008/084327 to M. Meurer et al.